Non-DNA-binding antibodies in patients with lupus nephritis could recognize membrane proteins of glomerular mesangial cells.

Lupus nephritis (LN) is a prototypic autoimmune disease, however, the precise immuno-pathogenesis of LN remains to be elucidated. In our previous studies, autoantibodies against mesangial cells had been identified in sera from patients with lupus nephritis and could bind the membrane proteins of human mesangial cells (HMC) directly through antigen-antibody interaction without DNA bridge. The current study is to investigate whether the autoantibodies were associated with anti-DNA antibodies and their target antigens distribution in different cell types. Sera from nine patients with renal biopsy proven lupus nephritis with positive anti-dsDNA antibodies and four healthy subjects were collected. IgG was isolated by Protein G affinity chromatography and then non-DNA-binding IgG fractions were obtained after deletion of anti-DNA antibodies using a DNA-cellulose affinity column. Membrane proteins, obtained from HMC, human umbilical vein endothelial cells (HUVEC), peripheral mononuclear cells by sonication and sequential centrifugation, were solubilized and applied in Western-blot analysis to characterize the target antigens. In results, the non-DNA-binding IgG fractions from sera of patients with lupus nephritis could blot the protein(s) of HMC membrane at 74, 63, and 42 kD. However, only a similar 74-kD protein could be blotted on membrane of HUVEC, and the target antigens on membranes of mononuclear cells were heterogeneous. In conclusion, our preliminary study had demonstrated that non-DNA binding autoantibodies against mesangial cells could be found in sera from patients with lupus nephritis. Although the target antigens might not be cell specific, the roles of these autoantibodies in the pathogenesis of lupus nephritis need further investigation.